In recent years, with the development of digitization techniques, a mode has been employed in which textual information and image information of newspapers, magazines, and the like are provided in the form of electronic data. This type of electronic data generally has a feature in which the content is viewed when displayed with a display device included in a personal computer or the like.
As the above display device which displays the electronic data, there is a portable display device as well as a stationary one. As a typical example of the portable display device, an e-book reader is given. The e-book reader is normally provided with a display portion on its front surface and a page-switching key on the periphery of its main body, which is operated to display data on the next page or the previous page on the display portion.
However, the e-book reader having the structure described above is handled very differently from paper media such as newspapers and magazines. An e-book reader is very different from a paper book especially in that pages are switched with key operation. Such a difference in the way they are handled causes the e-book reader a problem such as a lower efficiency of text reading, sentence comprehension, or image recognition than the paper media.
An e-book reader using a dual display device has been proposed in order to eliminate the above difference with paper media (e.g., see Patent Document 1 and Patent Document 2).